1. Field of the Invention
This invention relates to a method for treating oil, gas, and water injection wells with chemicals useful for reducing corrosion, scale, asphaltenes and other undesirable conditions, and a composition for practicing the method. This invention particularly relates to a method for the controlled placement of such chemicals, the controlled release of these chemicals, and a composition useful for practicing the method.
2. Background of the Art
Fluids produced from oil wells penetrating an oil-bearing formation primarily include crude oil and water and are herein referred to as formation fluids. A formation fluid may also contain natural gas which may or may not be desirable and may be the primary product of a given well in which case the well is referred to as a gas well. A formation fluid may also contain CO2 and will often contain oil and water insoluble compounds such as clay, silica, waxes, and asphaltenes, which exist as colloidal suspensions. In addition to the already listed components, formation fluids can also include inorganic components that can precipitate to form mineral scales These materials may be undesirable in the exploration for and production of oil and gas.
It is known in the art of oil and gas production to eliminate or mitigate the effects these undesirable materials. For example, during oil and gas production in production wells, the drilling of new wells, or workovers of existing wells, many chemicals, referred herein as “additives”, which include scale inhibitors, paraffin inhibitors, corrosion inhibitors and the like, are often injected from a surface source into the wells to treat the formation fluids flowing through such wells to prevent or control the precipitation of mineral scale, paraffins, and to protect the well against corrosion. These additives can be injected continuously or by batches through a conduit or tubing that is run from the surface to a known depth within the formation, typically upstream of the problem location. In addition, an additive can be injected into a near wellbore formation via a technique commonly referred to as “squeeze” treatment, from which the additive can be slowly released into the formation fluid. Sometimes, additives are introduced in connection with electrical submersible pumps, as shown for example in U.S. Pat. No. 4,582,131, or through an auxiliary line associated with a cable used with the electrical submersible pump, such as shown in U.S. Pat. No. 5,528,824. In addition, in wells without a packer in the completion, additives may be applied via pump or truck into the annular space between the tubing and the casing with a fluid flush driving the additive into the formation fluids.
In most of these operations, the additives are in the form of aqueous microemulsions or admixtures, although organic solutions are also known. The use of liquid additives is not without problems. In cold weather, the additives may freeze or gel during transportation or use. Supplying a source of heat, particularly for remote well sites can be a problem.
Supplying additives in the form of emulsions and solutions can also be an expense. Solutions and emulsions are, by their natures, composed of mostly inactive materials: water and/or solvents. It would be desirable in the art of treating oil wells to supply additives in a form that is economical to ship and handle and does not require co-shipping inactive components.
While using solid additives would seem to be a good means of avoiding the problems associated with additive solutions and emulsions, it too is not without problems. One such problem is metering solids. The metering of solids into an oil well could be both expensive and prone to blockages and other conditions requiring maintenance. One solution to this problem is disclosed in U.S. Pat. No. 6,326,335 B1, to Kowlaski, et al. Therein it is disclosed to prepare a microencapsulated additive wherein the additive is incorporated into a gelatin capsule, weighted with a heavy metal compound. In Kowlaski, the capsules are prepared to have a density such that they sink to the bottom of the well.
It would be desirable in the art of treating oil and gas wells with additives, to use solid additives that would release slowly with time. It would be particularly desirable to treat oil and gas well with solid additives that would not require heavy metals as weighting agents. It would also be particularly desirable in the art of treating oil and gas wells with additives to locate the additives at the point within the well that requires the treatment for which the additives are used.